Those verbs that undergo substantial changes when changing forms between tenses are irregular verbs. The changed forms of these verbs are often unrecognisably different from the originals. For example:

PRESENT TENSE

PAST TENSE

Go

Went

Run

Ran

Think

Thought

There is no way to tell what form an irregular verb is going to take in a changed tense; the only option for an English speaker is to commit the changes to memory. With practice, it will become a matter of habit.

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